A Beginner's Guide to the Internet/INTERNET.ISO/text/guides/help/ccmds.hlb

Text File | 1994-07-11 | 10.6 KB | 182 lines

Common Unix Commands

    Now, we'd like to give you a brief introduction to some of the
more commonly-used commands in the Unix system.  Most of these
commands have to do with the file system, but there are a few that
deal with other areas, such as other users on the system.

File System Commands

    There are a number of commands that allow you to view, copy,
move, erase, and organize files on the Unix system.
    The first command is ls, which is used to list the files that
are in the current directory.  DOS's dir command is much the same as
ls, but ls does offer some features that dir does not.  By itself, ls
just lists the files in several rows and columns.  Several useful
options can be given to ls to provide different output.  One option
that we find to be very useful is the -F option.  This option appends
symbols on to the end of certain files to indicate what type of file
it is.  The most common symbols are: / for directories and * for
executable files (programs).  Regular files do not have a symbol
appended to their name.  Another option that is used quite a lot is
the -l option, which produces a "long" display.  This format puts just
one file on each line, and it provides more detailed information about
each file, including its size, who owns it, and what permissions the
file has.  Permissions determine who has what access to a file.  See
the "chmod" command below for more information on permissions.  The
last option that is of interest is the -a option, which displays ALL
files.  In Unix, files whose names begin with a period are normally
"hidden".  Configuration files and other such files that the user
doesn't normally need to worry about are hidden in this way.  With the
-a option, however, you can see these files as well as normal ones.
For information on other options, such as sorting options, and
information on how to use "wildcards" in your commands, see the manual
page on ls (type "man ls").

    Next, we have three commands that deal with "directories".
Directories, which you may be familiar with if you've done work in
DOS, are a way of dividing up files into logical groups, which is
useful in organizing files.  If we didn't have directories on this
system, all of the thousands of files would be in one place.  Imagine
the mess!  Fortunately, we've got things organized into directories.
Directories are organized into a tree-like structure.  If you can
imagine the trunk of a tree spliting into several branches, which then
split into smaller branches, etc, then you can see how directories are
set up.  The topmost directory in this structure, from which all other
directories branch off, is called the "root" directory.  When you
first start using this system, you are given one directory (called
your "home" directory) that is given to you for your private use.
    To move from one directory to another, you use the "cd"
command.  To move into a directory that is within the current
directory, just type "cd dir", where "dir" is the name of the
directory you want to move into.  To move up one directory, type "cd
..".  And to move back to your home directory, type "cd ~".
    You can also create directories within your home directory to
help you organize your files.  For instance, you might want to create
a directory to hold files that you "FTP" from other locations until
you can download them.  The command to create directories is "mkdir".
So, in our example, you would start in your home directory (which is
where you will always be when you first login to the system), and type
"mkdir ftp".  This will create a directory called "ftp" in your home
directory.  Then, when you decide to retreive a file from a remote
system, just type "cd ftp" to move into that directory, and then run
the FTP program to get the file, which will be placed in the your ftp
directory.  A companion command, called "rmdir", will delete an empty
directory.  However, if there are files in the directory, rmdir will
not delete the directory.  See the section on the "rm" command below
for more information.

    Next is the "cp" command, which is pretty much the same as the
DOS "copy" command.  Simply type "cp source destination", and cp will
copy the first file to the second.  Often this is used to copy a file
to a different location, although it can also be used to generate a
copy of a file under a different name.
    The "mv" command has some similarities to the DOS "rename"
command, in that it can change the name of a file, but the mv command
can also move a file to a different location.  Simply the "mv old
new", and mv will either rename the file, or move it to the directory
specified.
    The "rm" command is much the same as the DOS "del" and "erase"
commands, but with a few notable features that DOS's commands lack.
Used without any options, rm will erase a file from the Unix file
system.  Be careful, however, because this is quite permanent once it
is done.  In recent years, DOS has given users the ability to
"undelete" files shortly after they have been deleted.  This ability
does not exist within the Unix system.  By default, the rm command is
set up to confirm before deleting a file.  This is set using the -i
option.  The rm command can also remove entire directory structures
using the -r option.  While the rmdir will only remove an empty
directory, the rm -r command will remove the entire directory,
contents and all.  Be VERY careful with this command, as it can
destroy a LOT of data very quickly and easily.

    The next command has to do with file permissions.  Permissions
determine which accounts have what access to a file.  For each file,
there are three different sets of three different permissions.  The
three sets are called owner, group, and world.  Owner refers to the
person to whom the file belongs, as displayed in a long file listing,
group refers to the group of users associated with the file, as
displayed in a long file listing, and world refers to everyone else on
the system.  For each of these sets, there are three possible
permissions: read, write, and execute.  Read means that set may read
the file, display its contents, and even copy it, write means that
set can modify the file, or even erase it, and execute means the file
is a program that can be run by that set.  Execute is also set if the
file is a directory, and gives members of that set certain abilities
with regard to the files in that directory.
    The command that is used to change these permissions is
"chmod".  For information on how to use this command, check the manual
page (type "man chmod" at the prompt).

    The next couple of commands could very well become your best
friends as you learn to use Unix and the Internet.  They give you
access to the online documentation for Unix, known as "manual pages".
The first command, apropos, takes a string to search for as an
argument.  It will then return a list of commands that match your
search string, with a short description of each command.  The man
command takes, as an argument, the name of a command, and displays the
manual page for that command via a "pager".  See the section on
more/less below for more information on pagers.  This is a good
facility to get information about specific commands in the Unix
system, and also to find commands that are related to certain topics.


    Similar to DOS's "type" command, Unix has a command called
"cat", which is used to dump the contents of a file to the screen.
Most users will probably find themselves using one of the "pager"
programs described below, as the cat program does not pause the
display for the user to read the information.  However, the cat
command is often useful at the beginning of a chain of commands to
feed input to the rest of the chain.  To dump a file's contents to the
screen with cat, simply type "cat file", where file is the name of the
file you with to display.
    The next two commands both serve the same purpose.  Both are
"pagers".  A pager is a program that displays its input one screenful
at a time, so that the information doesn't scroll past before you can
read it.  In addition, both of these pagers have functions to move
back a forth within the file being displayed, search for strings of
text within the file, and other useful features.  The first of these
commands is called "more" (named for the prompt it displays after each
page of text) which should be sufficient for the needs of most users.
The other command is "less" (a play on "more"), which has additional
features not found in more, which may appeal to more advanced users.
In both cases, you can simply type "more file" (or "less file") and
the pager will start displaying the file.  Also, in either pager,
pressing "h" at the prompt will display a short help file on the
various commands each pager provides.

    The last two commands that we will present here are used to
get information about other users who are online or who have accounts
on this system or other systems on the Internet.  The first command is
the "who" command.  If you type "who" at the prompt, it will dump a
list of the users who are logged into the system at the moment, with
information about when that user logged in, where they logged in from,
and other information.  A similar command, "w", also gives you an idea
of what each user is doing at the moment.
    The "finger" command can also display a list of who is online
at the moment, but is more useful when a user login name is given to
it.  This will produce information about that login name, such as: the
person's real name, when they last logged in or how long they've been
logged in, and even some personalized information, if the user has
chosen to provide this.  The personalized information is provided by
editing the ".plan" file in the user's home directory.  You could
provide some information about yourself, a witty quote, or whatever.
Give it a try!  Finger can also be used to lookup users on other
computers on the network.  Simply type the user's email address in
addition to their login name (ie. [e-mail]), and the
finger program will try to connect to the user's computer and return
information about the user.  For more information on the various
options available with the finger command, check out the manual page.

So, is that it?

    Not by a long shot.  Unix is a large and potentially complex
operating system.  It is also a very powerful operating system, once
you learn how to use it to its fullest potential.  If you are
interested in finding out more about Unix, we suggest you get a good
book on the subject.  Unix is becoming quite popular, and there are a
number of good books on the subject.  Until then, you can check out
all the help files we've provided, as well as the manual pages.  And,
if all else fails, send mail to help, and we'll do what we can to help
you out.  Good luck!